The present invention is directed generally to bunk support type boat trailers, and more particularly to those such bunk beam boat trailers where the side rails and other main structural members are constructed of aluminum. Boat trailers are presently found in Class 280, subclass 414.1 et seq.
Boat trailers, especially those trailers for carrying considerable weight, have typically been made of steel construction. The trailer frame side rails and cross members have been made of carbon or alloy steel materials which have required painting or galvanizing.
The use of steel materials and the additional surface preparation of the steel frame members has provided a trailer structure which is heavier than trailers of other metal construction, and which coated steel members generally loose their surface sheen appearance after short periods of exposure to water, especially salt water. Aluminum trailer frame construction has become common place on trailers used to carry lighter personal water craft (PWC) and small row boats. Aluminum alloys containing small amounts of chromium or molybdenum have superior surface sheen which lasts over long periods of water exposure. Aluminum frame construction also yields a lighter trailer which is easier to manipulate and has a lower towing weight than comparable steel construction.
Aluminum, however, does not have the same flexural characteristics as steel. It does not have the same elastic limits. Aluminum cannot be heat treated as steel can to increase its elasticity or bending strength. Being more brittle than steel, aluminum as a trailer frame construction material, has raised certain limitations in its use for larger trailers.
Trailer frame side rails, which generally utilize either tube construction or I-beam construction, are subjected to considerable bending and flexure, during over-the-road travel. These bending forces are concentrated on the unsupported middle span of the side rails. In bunk style trailers, this bending action is accentuated as the bunk beams are supported by the side rails at only two and sometimes three points. On support point has been forward of the axle assembly.
Therefore, in classic bunk trailer construction as is used for heavier loads, aluminum side rails would be subjected to severe bending forces which may lead to side rail failures. These load induced flexural forces when applied to the lighter weight aluminum trailer may also create unstable tracking of the trailer behind the towing vehicle.
What is desired is an aluminum frame bunk boat trailer construction where the frame loading is distributed to reduce and minimize bending forces on the frame side rails.
What is further desired is a bunk trailer construction where the major load forces are carried by the bunk assembly and transferred to the aluminum frame (side rails) in the region of the attachment of the wheel axle assembly, whereof said region is reinforced against bending forces.
What is also desired is a bunk trailer construction where the points of load forces and the points of support forces, on the aluminum frame side rails, are more evenly distributed to reduce the resultant bending forces especially in the unsupported middle section of the aluminum side rail's span.